A HIGHLY EFFICIENT AND RAPID TURNOVER OF COLLAGEN IN RAT PERIODONTAL TISSUES By J. SODEK

Collagen is the most abundant vertebrate protein and also the most important tensile component of connective tissue. The tensile strength of collagen fibres is derived from the uniform packing of tropocollagen subunits held rigidly together by intermolecular cross-links (Bailey et al., 1974). The collagen fibres provide a framework for the extracellular matrix of connective tissues, but, because of their rigid nature, the fibres must be remodelled by resorption and synthesis when changes in the size, shape or biophysical properties of connective tissue occur. Numerous studies, mostly carried out in rats, have shown that collagen turnover is quite rapid in connective tissues of growing animals (Kao et al., 1961a; Tanzer & Gross, 1964). However, turnover rates in the adult are greatly decreased (Kao et aL., 1961b), except in the uterus during pregnancy (Harkness & Harkness, 1954), in areas of wound healing (Grillo et al., 1958) and in some pathological conditions (Woessner, 1968), where collagen turnover is high. There is also some evidence suggesting a high collagen turnover in the periodontal tissues that support the teeth. This evidence comes from radioautographic studies (Carneiro & Leblond, 1966; Skougaard et al., 1970) and from the observation that in vitamin C deficiency the teeth loosen and may be lost (Hunt & Paynter, 1959). However, the radioautographic procedures lack specificity (Melcher & Eastoe, 1969) in labelling, and there are problems in good quantification (Rogers, 1973), whereas the evidence provided by vitamin C deficiency is indirect and is based on the knowledge that vitamin C is necessary for collagen synthesis (Barnes et al., 1970). To measure collagen turnover directly, radioactively labelled amino acids are used to label the collagen. If non-specific amino acids such as glycine